Speaking to The Guardian, Parker says of Sharp: "She is a strong woman. She came up through the military, she came up through a patriarchal system and she knows how to be in a room full of powerful men and demand respect."

"I don't think that this character is a sociopath, I think that she has a conscience."

Parker, whose previous credits include Dexter and Deadwood, added: "I think that she's a principled woman in terms of her point of view, her perspective as a soldier. That comes into play a little bit as the season goes on."

On the downsides of playing such a powerful character, she said: "It's almost like you can't then play a woman in power without addressing that, because it's part of our reality, in a way that it's just not for men.

"I don't think the men in power in this show ever get asked what it's like to be a man in politics."

Willimon said: "The way I approach each season is, let's not keep any great ideas in reserve - let's use them all. By the time it's the end of the season, we have no more ideas - in some ways, no idea how to keep the show going.

"We might have some notions of where it can go. [But] treat every season as though it's your last, don't hold anything back."